Maven说我在多模块项目中有一个循环引用，但不知道为什么 [英] Maven says I have a cyclic reference in multi-module project but can't figure out why

问题描述

我有一个如下所示的多模块项目:

I have a multi-module project that looks like this:

• 模块1
  • pom.xml
  • module1
    • pom.xml
    • pom.xml

    module2中的pom.xml对module1有依赖性.

    The pom.xml in module2 has a dependency on module1.

    当我运行mvn clean compile时，出现以下错误:

    When I run mvn clean compile I get the following error:

    反应堆中的项目包含循环引用.

    The projects in the reactor contain a cyclic reference.

    这是我在module1中的依赖项:

    Here are my dependencies in module1:

    <dependencies>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.14</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.6.1</version>
        </dependency>
        <dependency>
            <groupId>com.jcraft</groupId>
            <artifactId>jsch</artifactId>
            <version>0.1.48</version>
        </dependency>
    </dependencies>
    

    我不知道为什么它说有一个循环引用.即使当我在module1上执行mvndependency:tree时，我也会得到以下信息:

    I can't figure out why it says there is a cyclic reference. Even when I do mvn dependency:tree on module1 I get the following:

    [INFO] +- log4j:log4j:jar:1.2.14:compile
    [INFO] +- org.slf4j:slf4j-log4j12:jar:1.6.1:compile
    [INFO] |  \- org.slf4j:slf4j-api:jar:1.6.1:compile
    [INFO] +- com.jcraft:jsch:jar:0.1.48:compile
    [INFO] \- junit:junit:jar:4.8.2:test
    

    在我看来，在module1中没有任何对module2的引用.那么循环引用来自哪里?

    It looks to me like there aren't any references to module2 in module1. So where is the cyclic reference coming from?

    这是调试打开的日志:

    + Error stacktraces are turned on.
    Apache Maven 2.2.1 (r801777; 2009-08-06 15:16:01-0400)
    Java version: 1.6.0_31
    Default locale: en_US, platform encoding: Cp1252
    OS name: "windows 7" version: "6.1" arch: "amd64" Family: "windows"
    [INFO] Scanning for projects...
    [INFO] ------------------------------------------------------------------------
    [ERROR] BUILD FAILURE
    [INFO] ------------------------------------------------------------------------
    [INFO] The projects in the reactor contain a cyclic reference: Edge between 'Vertex{label='com.myorg:module2'}' and 'Vertex{label='com.myorg:module1'}' introduces to cycle in the graph com.myorg:module1 --> com.myorg:module2 --> com.myorg:module1
    [INFO] ------------------------------------------------------------------------
    [DEBUG] Trace
    org.apache.maven.BuildFailureException: The projects in the reactor contain a cyclic reference: Edge between 'Vertex{label='com.myorg:module2'}' and 'Vertex{label='com.myorg:module1'}' introduces to cycle in the graph com.myorg:module1 --> com.myorg:module2 --> com.myorg:module1
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:295)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:138)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:362)
    at org.apache.maven.cli.compat.CompatibleMain.main(CompatibleMain.java:60)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.codehaus.classworlds.Launcher.launchEnhanced(Launcher.java:315)
    at org.codehaus.classworlds.Launcher.launch(Launcher.java:255)
    at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:430)
    at org.codehaus.classworlds.Launcher.main(Launcher.java:375)
    Caused by: hidden.org.codehaus.plexus.util.dag.CycleDetectedException: Edge between 'Vertex{label='com.myorg:module2'}' and 'Vertex{label='com.myorg:module1'}' introduces to cycle in the graph com.myorg:module1 --> com.myorg:module2 --> com.myorg:module1
    at hidden.org.codehaus.plexus.util.dag.DAG.addEdge(DAG.java:143)
    at hidden.org.codehaus.plexus.util.dag.DAG.addEdge(DAG.java:123)
    at org.apache.maven.project.ProjectSorter.<init>(ProjectSorter.java:118)
    at org.apache.maven.execution.ReactorManager.<init>(ReactorManager.java:99)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:288)
    ... 11 more
    [INFO] ------------------------------------------------------------------------
    [INFO] Total time: < 1 second
    [INFO] Finished at: Thu Jul 05 17:21:21 EDT 2012    
    [INFO] Final Memory: 3M/244M
    [INFO] ------------------------------------------------------------------------
    

    推荐答案

    啊！这是一个误导性错误.

    Ah! It was a misleading error.

    问题不是模块1和模块2相互依赖.问题在于module2是一个Maven插件，在我的根pom.xml中，该部分中有该插件.我从构建中删除了该插件，它开始工作.

    The problem wasn't that there both module1 and module2 depended on each other. The problem was that module2 is a Maven plugin and in my root pom.xml I had the plugin in the section. I removed that plugin from the build and it started working.

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